Download REST API endpoints

[marcopeocchi]

Update: downloads REST API

Hello ✋,

This PR brings a new functionality asked in #70. Since the main focus is using the provided JSON-RPC interface the REST one will only bring limited funtionalities.

Group: /api/v1

Method	Route	Description
POST	/exec	Asynchronously starts a download
GET	/running	Gets running downloads

Examples

Start a download using /exec:

POST http://localhost:3033/api/v1/exec

Body

{
  "url": "https://...",
  "params": ["-N", "4", "-R", "infinite"] 
}

Returns The id of the download.

Refactor

The backend side has been entirely refactor starting from the last PR: fiber has been dropped for the standard library http package.

The reason behind this is because fiber was used soley for it's nice WebSockets API. Since I found gorilla's websockets which seamlessly integrates with the http package it was a no brainer. Moreover I don't like the philosophy behind fasthttp package. 🤠

Frontend side sees an improved rendering performance by cutting some unecessary useStates.
Anyhow is planned to migrate from redux to recoil or another atom base state manager to squeeze more performance.

Hopefully closes #70. 😎